There is a conventional valve unit for a hermetic reciprocating type compressor as illustrated in FIG. 1, and this valve unit is constituted as described below. That is, a cylinder head 1' with a discharge room 2' and a suction room (not shown) formed therein is installed on the top of a cylinder 3' in which a piston 4' performs reciprocating movements. Between the cylinder head 1' and the cylinder 3', there is installed a valve plate 10' in which a discharge passage 14' and a suction passage (not shown) are formed. On the top of the valve plate 10', there is installed a discharge valve 23' which performs closing/opening operations in such a manner as to discharge a compressed high pressure refrigerant gas during the elevation of the piston 4'. On the top of the discharge valve 23', there is installed a bending valve 22' which defines the closing/opening range of the discharge valve 23'. On the top of the bending valve 22', there is installed a stopper member 21' which regulates the operating ranges of the discharge and bending valves 23' and 22'.
The discharge valve 23', the bending valve 22' and the stopper member 21' are supported by guide pins 30', while, between the valve plate 10' and the cylinder 3', there is installed an elastic member 6A' having a suction valve 6' which is opened by a vacuum formed within the cylinder 3' during the time when the piston 4' moves from the upper dead point toward the lower dead point, i.e., during the suction stroke.
However, in the above described conventional valve unit for the hermetic reciprocating type compressor, when the piston 4' moves toward the lower dead point after the discharge valve 23' is closed at the upper dead point, a large amount of high compressed refrigerant gas remains within the discharge channel 14' after the closing of the discharge valve 23', so the formation of the vacuum state is delayed. Consequently, the suction valve 6' can not operate in an efficient manner, and therefore, a satisfactorily large amount of lower pressure refrigerant gas can not be sucked into the cylinder 3', with the result that the compressing efficiency is lowered.
Japanese Laid-Open Patent No. SHO 56-143375 discloses another hermetic reciprocating type compressor which has the same shortcoming as that described above, but which also describes a piston-drive mechanism. This compressor consists of a lower portion of vibrating elements and an upper portion of compressing elements. A connecting rod and a piston of the compressing elements are connected together by means of a ball joint, and a larger end of the connecting rod is fitted with a crank pin which is formed on the upper end of a driving shaft, while the driving shaft also serves as an eccentric oil supply pump. A partially cylindrical oil injecting member is installed at the end of the crank pin which is fitted with the large end of the connecting rod. The end of the oil injecting member is disposed axially inwardly relative to the end of the crank pin, while an oil supply hole which leads to the eccentric oil supply pump of the driving shaft is formed on the portion where the crank pin and the large end of the connecting rod are joined together. There are formed a plurality of oil injecting holes on the piston shaft in the radial direction. On the joining portion between the crank pin and the connecting rod, there is formed an oil channel for connecting the oil supply hole and the oil injecting holes.
In the above described hermetic reciprocating type compressor, an oil supplying mechanism is formed on the peak of the crank pin, so that the oil flow should be made constant, and all of the flowing oil should be supplied to the piston thereby providing a lubrication of the ball joint, reducing the friction loss to a significant degree, and improving the compressing efficiency. Further, owing to the cooling effect of the oil, the gas within the cylinder is compressed at a uniform temperature, thereby improving the compressing efficiency in an indirect manner. Further the oil which is supplied from the large end of the connecting rod is injected directly through the oil injecting holes of the relief portion of the crank pin to the wall of the hermetic container, and therefore, the temperature of the contained gas can be maintained at a low level.
However, when the piston moves toward the lower dead point after the closing of the valve at the upper dead point, an excessively large amount of high pressure refrigerant gas remains within the discharge passage after the closing of the discharge valve, and therefore, the formation of vacuum within the cylinder is delayed for the reasons noted earlier with respect to the apparatus of FIG. 1. Accordingly, the suction valve can not operate in an efficient way, so that it should be impossible to suck a large amount of low pressure refrigerant into the cylinder, thereby aggravating the compressing efficiency.